Roslyn-Backed MCP Server

Local-first MCP (Model Context Protocol) server for semantic C# analysis, navigation, validation, and refactoring on real .sln / .slnx / .csproj workspaces. It uses Roslyn and MSBuildWorkspace, runs over stdio, and does not require Visual Studio.

What It Does

• Loads real C# solutions and projects with session-scoped workspaceIds.
• Exposes semantic navigation, diagnostics, build/test helpers, and preview/apply refactoring workflows over MCP.
• Ships as a .NET global tool, a Claude Code plugin, and a source-buildable stdio host.
• Publishes the authoritative live surface through server_info and roslyn://server/catalog.

Quick Start

Prerequisites

• .NET 10 SDK — pinned to 10.0.100 in global.json (rollForward: latestFeature)

Install As A Global Tool

dotnet tool install -g Darylmcd.RoslynMcp

• Package ID: Darylmcd.RoslynMcp
• CLI command: roslynmcp

Build And Run From Source

dotnet build RoslynMcp.slnx --nologo
dotnet test RoslynMcp.slnx --nologo
dotnet run --project src/RoslynMcp.Host.Stdio

Claude Code Plugin

/plugin marketplace add darylmcd/Roslyn-Backed-MCP
/plugin install roslyn-mcp@roslyn-mcp-marketplace

The plugin bundles the MCP server, 32 skills, and safety hooks. For packaging, reinstall, and local plugin-dev details, see docs/setup.md and docs/reinstall.md.

Any Stdio MCP Client

Point the client at the installed tool:

{
  "mcpServers": {
    "roslyn": {
      "type": "stdio",
      "command": "roslynmcp"
    }
  }
}

For NDJSON framing, handshake order, and minimal Python/C# client examples, see docs/stdio-client-integration.md.

MCP Registry (submission pending)

The server is also being published to the public MCP Registry. Once the submission is approved, MCP-Registry-aware clients will be able to discover and install the server by name.

Draft manifest: .claude-plugin/server.json — published name io.github.darylmcd/roslyn-mcp, NuGet package Darylmcd.RoslynMcp, runtime dnx.

Until the submission is approved, prefer the Global Tool or Claude Code Plugin install paths above. After approval, this section will be updated with the registry URL and the registry-aware client install snippet.

Configuration

The server starts with built-in defaults. To override ROSLYNMCP_* values for a repo, add a project-scope .mcp.json with literal env values.

Variable	Default	Purpose
ROSLYNMCP_MAX_WORKSPACES	8	Concurrent workspace cap
ROSLYNMCP_BUILD_TIMEOUT_SECONDS	300	Build timeout
ROSLYNMCP_TEST_TIMEOUT_SECONDS	600	Test timeout
ROSLYNMCP_PREVIEW_TTL_MINUTES	5	Preview-token TTL
ROSLYNMCP_REQUEST_TIMEOUT_SECONDS	120	Per-request timeout

Copy-ready examples live in docs/mcp-json-examples/README.md. The full runtime/config surface is documented in ai_docs/runtime.md.

Security

Loading a solution or project executes MSBuild evaluation. Treat workspaces as trusted code unless you run the server inside a sandbox, container, or VM.

• Only load repos you trust.
• Use isolation for untrusted workspaces.
• Path validation is defense in depth, not a substitute for trusting the loaded project graph.

See SECURITY.md for disclosure policy.

Live Surface

The current release exposes 168 tools (111 stable / 57 experimental), 13 resources (9 stable / 4 experimental), and 20 prompts (all experimental).

Use the running server for the authoritative live catalog and support tiers:

• server_info for a human-readable summary
• roslyn://server/catalog for the machine-readable contract
• roslyn://server/resource-templates for resource URI templates

Stable families include workspace/session management, semantic navigation, diagnostics, build/test helpers, and preview/apply refactoring flows. Experimental families include broader project mutation, scaffolding, orchestration, direct text-edit helpers, and prompts.

Repository Layout

• src/RoslynMcp.Host.Stdio/ — stdio host, tool/resource/prompt wiring, logging
• src/RoslynMcp.Core/ — DTOs, contracts, abstractions, preview-store types
• src/RoslynMcp.Roslyn/ — Roslyn workspace, analysis, diagnostics, refactoring, execution services
• tests/RoslynMcp.Tests/ — integration and regression coverage
• skills/ — bundled Claude Code skill definitions
• hooks/ — Claude Code safety hooks

Docs

• docs/setup.md — packaging, Docker, tool install, plugin install, CI artifacts
• docs/stdio-client-integration.md — custom MCP client integration
• docs/product-contract.md — stable vs experimental surface contract
• docs/release-policy.md — release gates and compatibility rules
• AGENTS.md — bootstrap entry point for AI agents working in this repo
• ai_docs/README.md — canonical AI-doc routing index

Support

• Bugs and feature requests: GitHub Issues
• Contribution guidelines: CONTRIBUTING.md
• Security disclosures: SECURITY.md